Bash is a POSIX shell (sh(1) compatible) command interpreter. Many useful features have been added with inspiration drawn from the Korn & C shells. New and unique extensions are occasionally added to the shell. There is also support for custom run-time extensions via the enable builtin command. Bash may be compiled to be POSIX compliant by default as specified by the Shell and Utilities portion of the POSIX specification (IEEE Standard 1003.1).